Monitoring of chemical additives

Abstract: A method for allowing authentification of a bulk liquid e.g. petrol or another mineral oil based product, comprises introducing into the liquid a small amount of a chemiluminescent substance. Samples for authentification are subjected to the conditions required to trigger the chemiluminescent reaction and monitored for chemiluminescent emission.

Description: This invention relates to a method for monitoring the levels of chemical marker compounds. The invention is particularly, but not exclusively, directed towards the detection of added chemicals in liquid products, especially in oil based products such as petroleum. Chemical additives are important constituents of oil based products such as petroleum, diesel oil and lubricating oils. The additives are generally designed to impart favourable and occasionally unique properties to the product such that their absence or a reduction in their concentration may result in a significant loss of performance. These additives are normally introduced at a central distribution point into products which may be distributed on a world wide basis. Since product performance is dependent on the presence of appropriate levels of the additives in the final product as it is retailed, a system for demonstrating their presence at any point in the distribution chain is required. A second, but equally important consideration, relates to the problem of counterfeiting. Products which are perceived to have favourable properties over rival products will be imitated for reasons of commercial gain. They may not, for example, enjoy the benefits of the correct additives but may be sold as to imitate visually the better product. In such a situation, the ability to distinguish the genuine product from imitations is highly desirable. Accurate identification of oil based products is also important since litigation can be brought as a consequence of accidents and spillages. In these situations, the presence of a marker substance which can identify or alternatively exclude a particular manufacturer or distributor can be of extreme value. In summary, the presence of readily identifiable marker substances in oil based products could contribute significantly to several aspects of quality assurance in the oil and petroleum industry. Up to now, it appears that no simple procedure has yet been devised to provide such a system. Fuel additives are frequently beneficial to the performance of the product at extremely low concentrations. However, their incorporation into fuels at such low concentrations means that they are not readily detected by conventional analytical procedures. Even in situations where the additive can be detected by sophisticated physical/chemical techniques, there is the problem that samples must be taken to a central laboratory for analysis which may be tedious and time consuming. One recent approach has been to make use of the fact that many organic compounds are immunogenic so that immunological assay methods can be applied to their detection (see for example EP-A-0327163). Though these methods do possess inherently high sensitivities, they are not intrinsically simple to perform and therefore do not lend themselves to analysis in the field. Moreover, they involve the use of monoclonal antibodies which may lack the stability of simple chemicals, again restricting the site or scope of application. This approach relies on subjecting a small sample to an assay procedure to quantify the additive compound of interest; there is no suggestion of introducing a chemical marker to the bulk product or along the distribution chain at source which is subsequently triggered possibly many weeks later several steps down the distribution chain to allow analysis or detection thereof. We have developed a radically different approach which uses an independent substance which has some unique, easily detected property and which can be added to the fuel at source or along the distribution chain as a marker along with the additives. The marker should possess certain characteristics. Firstly, it should partition into the organic phase so that contact with water, as might occur for example in a storage vessel, will not cause substantial partitioning into the aqueous phase. Secondly, the marker compound should remain stable in the fuel for several weeks without substantial alteration of its detection characteristics. Thirdly, the marker compound should be reproducibly detectable at extremely low concentrations, partly for reasons of cost but also to ensure that it does not itself interfere with the performance of the fuel. The marker compound should be detectable quantitatively with a simple detection system. Finally, neither the fuel itself or any other additive should interfere significantly with the behaviour of the marker under normal analytical conditions. Accordingly, in one aspect of this invention, there is provided a method for authenticating a bulk liquid, which comprises introducing into said bulk liquid a chemiluminescent substance capable of taking part in a chemiluminescent reaction, withdrawing a sample of said bulk liquid to be authenticated, exposing said sample to the conditions required to trigger a chemiluminescent reaction and authenticating said bulk liquid based on whether said chemiluminescent reaction occurs. Chemiluminescent compounds have the property that, under defined conditions, they can be induced to emit light. This process can involve activation of a reaction by the supply of heat to the compound or alternatively may involve a simple chemical triggering mechanism. The light emission can be detected or quantified using a simple photon counting device. One potential advantage of chemiluminescence is that, generally, endogenous chemiluminescence is low so that a small signal can be readily detected against a very low background. The term "bulk liquid" is used to define any liquid to be authenticated. Whilst primarily intended to cover industrial liquids such as mineral oils intended to be supplied in large volumes, the term is also intended to embrace liquids supplied in small volumes, other than for analytical purposes. The chemiluminescent substance may be any suitable substance which retains at least some of its chemiluminescence when introduced into said bulk liquid, and includes those chemiluminescent materials referred to as bioluminescent. The terms "chemiluminescent substance" and the like should be interpreted broadly as including chemiluminescent compounds as well as cofactors, catalysts or other substances capable of taking part in a chemiluminescent reaction of the bulk liquid. The authentication of the bulk liquid may be by reference to the extent of dilution thereof, wherein said introducing step comprises introducing into said undiluted bulk liquid a known amount of a chemiluminescent substance, and said authentication step comprises monitoring the characteristics of said chemiluminescent reaction and comparing said characteristics with those of a chemiluminescent reaction in the undiluted bulk liquid, to determine the extent of dilution of said bulk liquid. In a further aspect, the authentication may be by detecting the presence or amount of an additive or mixture of additives in the bulk liquid, wherein the amount of said chemiluminescent substance introduced into the bulk liquid is related to the amount of said additive, or mixture of additives. Said chemiluminescent marker substance is preferably introduced into said bulk liquid with said additive. The methods of this invention are particularly useful when said bulk liquid is a mineral oil based product, although it may be any industrial or non-industrial liquid. Thus, the methods of this invention relate to the use of a chemiluminescent marker which can be incorporated into the fuel at sufficiently low concentrations that it does not affect performance, and which can also be reliably detected using a simple analytical kit. A preferred aspect of the invention involves the use of chemiluminescent acridinium compounds which have inherently high quantum yields and can therefore be detected with extremely high sensitivity. The application of these compounds as labels for substances of biological interest is disclosed in UK-B-2112779. Somewhat surprisingly, certain acridinium compounds can be detected with high sensitivity in petroleum by means of addition of simple oxidising reagents, the light output being directly proportional to the concentration of acridinium compound in the sample. A critical observation is that a 10µl sample of petrol yielded no significant chemiluminescence when subjected to the reagents used to generate the light emitting reaction. The chemiluminescent marker substance is preferably an acridinium compound capable of undergoing a chemiluminescent reaction and of the general formula:- wherein R 1 is a moiety capable of being part of a quaternary nitrogen centre, for example an alkyl, alkenyl, alkynyl, alkoxyl or aryl containing group; R 2 and R 3 may be the same as R 1 or a hydroxyl, carboxyl, amino, substituted amino or halide group; R 4 is a moiety whose chemical reactivity permits the compound to undergo a chemiluminescent reaction, and X - is an anion. The chemiluminescent marker substance is substantially insoluble in water. Said chemiluminescent marker substance is preferably present in said bulk liquid in an amount between 0.001 ng/µl and 10 ng/µl, and preferably is immunologically unbound in normal use of said bulk liquid. An additive formulation for a bulk liquid for use in a method as decribed above may contain one or more ingredients for modifying or enhancing one or more selected properties of the bulk liquid, in combination with an amount of a chemiluminescent marker substance. The observed characteristics may comprise one or more of wavelength, intensity, variation of intensity with time, other kinetic variations, and polarisation. The invention may make use of other chemiluminescent compounds such as (though not exclusively) phthalhydrazides and their derivatives, phenanthridinium and quinolinium salts, bis-acridinium salts, bis-oxalate esters, dioxetanes and organometallic compounds such as ruthenium chelates. The structures of numerous chemiluminescent compounds are recited in the literature and the selection of suitable compounds in accordance with the detailed criteria contained herein is well within the competance of one skilled in the art. Our experiments have shown that such compounds may be stored in petroleum for significant periods of time with no loss of chemiluminescent properties. Moreover, we have found that such compounds can be designed so that they will not partition into water should such contamination be present in storage vessels. Finally we have been able to detect as little as 1.2 parts/billion of the acridinium compound in 10µl of petroleum. These observations demonstrate that chemiluminescent molecules and in particular acridinium compounds can be used as marker substances in petroleum based products. It is thus possible to add such compounds to petrol at the same time as other, performance related additives are being introduced. Analysis of the amount of chemiluminescent substance at any point in the distribution chain will thus provide an indication that such addition has been made and also that the fuel has not been diluted with other base fuel. Moreover, the presence of the chemiluminescent molecule in the fuel will indicate that the fuel is the genuine manufactured material. In practice, as little as 1g of a chemiluminescent acridinium derivative can be added to a volume of 1.5 million litres of petroleum and be readily detected after a period of 6 weeks in only 10 µl of fuel. At the concentration of acridinium compound present, there is no detectable effect of the marker on performance. Thus, at this stage, it appears that the use of chemiluminescent markers in fuel offers a simple, reliable and sensitive method for monitoring additive levels. A test kit may be used for the monitoring of additive levels under field conditions. Luminometers capable of detecting low levels of light emission have been available for several years, though most such instruments are designed for routine laboratory use. Hand held devices have been developed which are capable of reading the light emission from constant sources by means of a photographic plate. In this aspect, a luminescence detector is provided including injection devices capable of delivering the reagents necessary to initiate the chemiluminescent reaction. The detector is preferably capable of fitting into a compartment no bigger than a brief case. The light emission is recorded and, if below a certain threshold, will alert the operator to the possibility that the additive level is inadequate. Further tests can then be undertaken in the laboratory to determine the exact nature of the defective level. The invention will now be further described with reference to the following example:- Example The following compounds (1) and (2) were prepared by standard methods:- Approximately one hundred µg of each compound were dissolved in 10 ml of dry acetonitrile. Ten µl of each solution were then diluted to a volume of 1 ml with standard unleaded petrol to give a final concentration of acridinium salt of approximately 100 ng/ml. These samples were then stored at room temperature in the dark and, at intervals, 10 µl aliquots of these were removed to measure chemiluminescence. Measurements were carried out in a Berthold "Klinilumat" Luminometer. The chemiluminescent reaction was initiated by injection of 0.3 ml of a solution of 1% hydrogen peroxide in 0.1 M nitric acid followed by 0.3 ml of a solution of 1.0% sodium hydroxide containing 0.2% cetyltrimethylammonium chloride. Luminescence output was integrated over a suitable interval and results obtained after different periods of storage were as follows: Compound 1 Time Light Yield (RLU) Day 1 1.5 x 10 7 Day 10 1.5 x 10 7 Day 27 1.4 x 10 7 Day 33 1.3 x 10 7 Day 40 1.3 x 10 7 Compound 2 Day 1 2.4 x 10 7 Day 2 2.3 x 10 7 Day 4 2.4 x 10 7 Day 10 2.5 x 10 7 Day 17 2.0 x 10 7 These results show that when either of these compounds is added to standard unleaded petrol, chemiluminescence can be recovered quantitatively within reasonable limits of experimental error over a significant time period.

Claims: A method for authenticating a bulk liquid, which comprises introducing into said bulk liquid a chemiluminescent substance capable of taking part in a chemiluminescent reaction, withdrawing a sample of said bulk liquid to be authenticated, exposing said sample to the conditions required to trigger a chemiluminescent reaction, and authenticating said bulk liquid based on whether said chemiluminescent reaction occurs. A method according to Claim 1, for authenticating said bulk liquid by reference to the extent of dilution thereof, wherein said introducing step comprises introducing into said undiluted bulk liquid a known amount of a chemiluminescent substance, and said authentication step comprises monitoring the characteristics of said chemiluminescent reaction and comparing said characteristics with those of the chemiluminescent reaction in the undiluted bulk liquid, thereby to determine the extent of dilution of said bulk liquid. A method according to Claim 1, for authenticating said bulk liquid by determining the presence or amount of an additive or mixture of additives therein, wherein the amount of said chemiluminescent substance introduced into the bulk liquid is related to the amount of said additive or mixture of additives. A method according to Claim 3, wherein said chemiluminescent marker substance is introduced into said bulk liquid with said additive or mixture of additives. A method according to any preceding of the claims, wherein said bulk liquid is a mineral oil based product. A method according to Claim 5, wherein said product is selected from the group comprising petroleum, diesel oil and lubricating oils. A method according to any preceding claim, wherein said chemiluminescent marker substance is an acridinium compound capable of undergoing a chemiluminescent reaction and of the general formula:- wherein R 1 is a moiety capable of being part of a quaternary nitrogen centre, R 2 and R 3 may be the same as R 1 or a hydroxyl, carboxyl, amino, substituted amino or halide group, R 4 is a moiety whose chemical reactivity permits the compound to undergo a chemiluminescent reaction, and X - is an anion. A method according to any preceding claim, wherein said chemiluminescent marker substance is substantially insoluble in water. A method according to any of the preceding Claims, wherein said chemiluminescent substance is present in said bulk liquid in an amount between 0.001 ng/µl and 10 ng/µl. A method according to any of the preceding Claims, wherein said chemiluminescent substance is immunologically unbound in normal use of said bulk liquid.

Inventors: HERBERT SIAN AERONA, WEEKS IAN DR, HERBERT, SIAN AERONA, WEEKS, IAN, DR.
Applicants: MOLECULAR LIGHT TECHNOLOGY LTD, MOLECULAR LIGHT TECHNOLOGY LIMITED
Application year: 1994
Main classification: G01N21
IPC codes: G01N21, C10L1, G01N33, C10M171, C10M177